1. Field of the Invention
The present invention relates to a shift device with a synchronizer for a transmission in which pressing force applied to a shift sleeve can be amplified into larger pressing force acting on a synchronizer ring while gears of the transmission are shifted, thereby reducing operating force necessary for a driver or an actuator.
2. Description of the Related Art
A shift device with a synchronizer for a transmission of this kind is disclosed in Japanese unexamined patent application publication No. 09-89002. This conventional shift device is used to shift gears between fifth-speed and reverse speed. It has a hub, a shift sleeve, a synchronizer ring capable of being pressed toward a fifth-speed gear, and a plurality of lever members provided between the synchronizer ring and the hub. The lever members change an axial pressing force from the shift sleeve into an amplified axial pressing force that acts on the synchronizer ring when the sleeve is being moved toward the fifth-speed gear, and they transmit the axial pressing force from the sleeve toward the reverse gear (in an opposite direction to the fifth-speed gear) to the fifth-speed gear so that the synchronizer ring and the fifth-speed gear are synchronized. This enables the sleeve rotating due to inertia of a clutch disc to stop the rotation thereof, and then the sleeve is smoothly engaged with the reverse gear. Thus the shift device can be a simple device using the lever members at lower manufacturing costs to decrease gear engagement noise in a shift operation to the reverse-speed position.
In the shift operation to the reverse-speed position, the friction torque of the synchronizer ring presses the lever members to extend them outwardly in the radial direction to prevent the sleeve from further advancing before the synchronization between the fifth-speed gear and the sleeve is ended.
When the synchronization is ended, the blocking force of the synchronizer ring due to the friction torque vanishes. Accordingly, the slanted surfaces formed on the inner surface of the sleeve press the lever members inwardly in the radial direction, so that the sleeve moves toward and engages with the reverse gear.
Another shift device with a synchronizer for a transmission of this kind is disclosed in Japanese unexamined patent application publication No. 2002-174261.
This conventional shift device has a plurality of lever members that are arranged at an axial middle position of a hub. The lever members are formed to be smaller to improve a shift feeling by decreasing operating force to push the lever members to an inner side after synchronization is ended to move a shift sleeve toward a high-speed gear in a shift operation at a high rotation speed. The same lever members are used to obtain in the synchronization toward one of the speed gears and the other thereof.
These conventional shift devices with the synchronizer, however, encounter the following problems.
In the former conventional device, the lever members thereof are inserted into a recessed portion (a groove portion formed in a circumferential direction) of the hub, being formed in an appropriately semicircular arc-like shape in a front view. This causes the lever members to become larger in the circumferential direction thereof. The thickness thereof needs to be larger to ensure the necessary stiffness, and accordingly they become heavier to generate larger centrifugal force that acts on the lever members during a shift operation at a high rotational speed. The larger centrifugal force causes a driver's operating force for moving the shift sleeve to be larger when it presses the lever members toward the inner side after the synchronization is ended. Therefore, the former conventional device cannot avoid from the deterioration in a shift feeling.
On the other hand, the latter conventional device can avoid from the deterioration in the shift feeling at the high rotational speed by using the lever members that are small in size and lighter in weight. The top portions of the lever members are, however, easily disengaged from inner splines of the shift sleeve when the lever members sometimes happen to be inclined toward a speed gear arranged at the one side in a state where the sleeve is engaged with another speed gear arranged at the opposite side. To avoid this problem, the shift sleeve needs to be formed larger in an axial direction thereof.
It is, therefore, an object of the present invention is to provide a shift device with a synchronizer for a transmission which overcomes the foregoing drawbacks and in which can decrease the both of the length in a circumferential direction of lever members and the axial length of a shift sleeve, ensuring a good shift feeling.